1. Field of the Invention
The present invention relates to a position controlling apparatus and method for an elevator, and more particularly to a position controlling apparatus and method for an elevator which minimizes a levelling error of a floor level and a car bottom level when an elevator arrives at an destination floor.
2. Description of the Conventional Art
FIG. 1 schematically illustrates a conventional elevator system. As shown therein, an elevator car 101 moves along an hoist way in a building and in the elevator car 101, there are provided with a plurality of destination floor selecting buttons (not shown) for a passenger to select a desired floor according to the number of elevator operating floors. Also, although not shown in the diagram, there are provided with a plurality of hall call buttons to supply a signal which indicates a hall call of a passenger on a hall of each floor. A counter weight 102 and the elevator car 101 are connected to each other by a rope of which an end is fixed to the counter weight 102 and the other end to the elevator car 101. A sheave 105 moves the elevator car 101 by winding or releasing the rope. An AC (alternating current) motor 106 is coupled to the sheave 105 for thereby driving the sheave 105, and an encoder 107 supplies a pulse signal corresponding to the rotation of the AC motor 106. In addition, a position detector 103 which is arranged on an upper surface of the elevator car 101 detects that the elevator car arrives at a previously determined position of each floor and outputs a signal indicating the detection. Further, a shielding board 104 is provided at a predetermined position of each floor to operate the position detector 103. Generally, a switching device such as a photo coupler, which has a light emitting unit and a light receiving unit, is used for the position detector 103. When the shielding board 104 which is positioned between the light emitting unit and the light receiving unit of the position detector 103 shields light, the switching device connected to the light receiving unit becomes on or off, thereby indicating the light shielding and accordingly indicating that the elevator car 101 has arrived at the predetermined floor. Here, an output signal of the position detector 103 is transmitted to an operation controller 108. The operation controller 108 determines a floor for the elevator car 101 to serve, when it receives hall call signal or a car call signal from one of the hall call buttons or the destination floor selecting buttons. Then, the operation controller 108 computes a distance-to-go in accordance with a distance of a present floor from a base floor for example a 1st floor and a distance of a destination floor from said base floor, and outputs velocity command signal corresponding to the computed distance-to-go.
The motor controller 109 outputs a current control signal or a voltage control signal corresponding to the velocity command signal from the controller 108. Since the current control signal or the voltage control signal from the motor controller 109 is a direct current signal or a direct voltage signal, when an alternating current motor is used as a driving motor for an elevator, above said direct current signal or direct voltage signal is outputted to the motor 106 via an inverter 110. The inverter 110 outputs an alternating control signal having variable amplitude and frequency to the motor 106 correspondingly to the control output of the motor controller 109.
In order to monitor whether a velocity and position of a car is being controlled correspondingly to said velocity command signal, pulse signal indicating rotation and rotating direction from said encoder 107 is fed back to said motor controller 109.
Here, in the conventional art, a technique of generating the velocity command signal by the operation controller 108 has several methods.
A first method is to multiply the distance to go by a gain value. However, according to the method, it is difficult to compute an accurate gain value because the distance and the velocity have different units, and such a method has a problem that the gain value should be always adjusted because the gain value varies in accordance with the motor, load of the elevator car, a standard speed thereof and kinds of traction machine (including a motor, a decelerator and a sheave).
A second method is to calculate a velocity command value using the formula, that is, the velocity command value=a current velocity command value+gain (a previous velocity command value-feedback speed). However, since such a method is to control actual speed of the elevator to follow the velocity command, it is more suitable to the controlling of the speed of the elevator, rather than the controlling of the position thereof, and also, similarly to the above first method, the problem of the adjusting of the gain still can not be solved.
Third, there is provided a method which computes a velocity command, corresponding to a distance-to-go, to follow velocity profiles of an acceleration profile region, a uniform velocity profile region and a deceleration profile region and, when having a synchronization position error between a position of the elevator car obtained by counting a pulse number of the encoder and an actual position thereof obtained by the position detector, obtaining a new distance-to-go by adding the error to the previous distance-to-go, and on the basis of the newly obtained distance-to-go computing a new velocity command value in ranges of only the acceleration profile region and the uniform velocity profile region. Such a method suggested by the applicant of the invention in U.S. Pat. No. 5,896,950. However, it is impossible to solve the problem of having a difference between a bottom level of the elevator car and a level of a landing in the arrival of the elevator at the desired floor, since according to this method when the synchronization position error is produced in the deceleration profile region, the error can not be corrected.
Lastly, there is a method for obtaining the velocity command value which sets up a database of a synchronization position error quantity with respect to an entire velocity region including the acceleration profile region, the uniform velocity profile region and the deceleration profile region by each item of the load, the moving direction, the starting floor and the stopping floor of the elevator car, and then continuously updating the database while operating the elevator. Such a method may solve a problem of a levelling error in the arrival of the desired floor due to the synchronization location error to the entire velocity profile region. But, a memory of a large capacity is required to accomplish the above method, and a complex program should be operated in order to correct the error and update the database, which results in high possibility of having an erroneous operation due to bugs or noises of the program.